The present invention relates to an automatic sharpening-free pencil, particularly a non-sharpening pencil with retractable presharpened pencil lead elements.
Conventionally each non-sharpening pencil is composed of a casing with an opening at each end, a plurality of plastic lead holders each fixed with a presharpened pencil lead element stacked in axial alignment within the casing so that, by pushing its top lead holder, the lowest lead holder with a presharpened pencil lead element can be pushed out of the casing for writing purpose. In such a design, the plastic lead holders occupy a considerable space within the casing, and thus the quantity of presharpened pencil lead elements which the casing can hold is limited. Also, the service life of the non-sharpening pencil is shortened. Moreover, the loss of any pencil lead holder will make the whole non-sharpening pencil useless.
U.S. Pat. No. 4,320,982 to Kuo, the inventor of the present application, discloses a writing implement comprising an outer casing, a coil spring disposed within the casing, an inner tube inserted through the coil spring with a plurality of presharpened pieces of pencil lead stored therewithin, and a capping member fitted over an open end of the inner tube. The lower (writing) portion of the inner tube is split into two clamping halves. The lower end of the coil spring is formed into a hook which slides along the slot formed between the clamping halves to allow the expulsion and feeding of presharpened pieces of pencil lead into the space between said two clamping halves. Without any means to retract the presharpened pencil lead into the inner casing, the writing apparatus disclosed by such a writing implement is risky when it is placed with its presharpened pencil lead facing upward or when it is pointing to any person. The presharpened pencil lead may cause injury to the eyes or other important organs.
The U.S. Pat. No. 4,966,478 to Kuo, the inventor of the present application, discloses a writing implement which can have its presharpened pencil lead retracted. By pushing a press portion, an elastic hook means is displaced outwards in order to retract the extended presharpened pencil lead element into the inner cylinder. However, when the press portion is pushed, a stress is concentrated at the junction between the press portion and the elastic hook-means, subjecting the junction to breakage after several pushing movements for retraction of the pencil lead element. Moreover, after retraction of the pencil lead element, the elastic hook means can't resume its original position but remains projected outward in a tensed condition because it is restricted by the lowest presharpened pencil lead element. The tensed condition brings an inner stress at the elastic hook means, and prolonged inner stress will result in elastic fatigue so that the service life of the non-sharpening pencil is shortened. To eliminate the above two defects, the elastic hook means must be made of plastic material with high elastic coefficient to prevent it from breakage due to fatigue caused by prolonged existence of stress. Furthermore, the outward projection of the elastic hook means adversely affects the appearance of the writing apparatus.